In prior art, adaptive front lighting systems (further also referred to as AFS) of motor vehicles are known where the swivel angles of the headlamps are determined based on the values of the steering wheel angle and the vehicle speed. Accordingly, the swivel angles are only based on the sensed instantaneous path of the vehicle. In some drive scenarios, however, such as just before the vehicle enters or exits a curve, or during passing a curve with a changing radius of curvature, or having an S-shaped curvature, the instantaneous vehicle path sensed in this way is not entirely indicative of the road path in front of the vehicle. It is particularly advantageous for the performance of the headlamps to predictively illuminate the upcoming road in drive scenarios when the road varies from the current vehicle path.
Generic AFS systems that predictively calculate upcoming vehicle path data to optimally manipulate the beam pattern of the headlamps include at least two headlamps, each with a swivel mechanism and a controller. The headlamps cooperatively project a beam pattern for illumination of the road upcoming in front of the vehicle. The swivel mechanisms change the respective swivel angle of each headlamp.
Therefore, the AFS systems of prior art, which for manipulating the headlamps are based only on the steering wheel angle and the vehicle speed, are characterized in that the headlamps cannot be swiveled into the position that is optimal for the future vehicle path, but illuminate the area immediately in front of the vehicle so that even glare for the oncoming traffic may be created. Even if the instantaneous measurement is filtered and dead zones are applied to overcome any jittering in the steering angle measurement resulting from the lane adjustments by the driver, the illumination will still not be optimal. Moreover, filtering and dead zoning operations delay performance of a conventional AFS.
Further developments of the AFS resulted in systems that swivel the headlamps already before the vehicle enters the curve so that the visibility of the upcoming curve is improved. Also, the headlamps are swiveled back into the initial position, i.e. the straight ahead position already during exiting the curve so that the upcoming straight segment of the road is visible better. In this way, glare for the oncoming traffic is avoided in each case, but illumination of the road is not optimal.
Similarly, unfavorable illuminations of the road result when passing S-shaped roads or changing the lane. When passing S-curves, it is necessary to swivel the headlamps in the direction of the upcoming curve before the saddle point of the S-curve is reached so that the visibility of the upcoming curve is improved.
Such a further developed predictive adaptive front lighting system for a motor vehicle, for example, is disclosed by DE 10 2008 000 769 A1. Here, the controller of the system receives vehicle position data from, for example, a GPS system as well as data that relate to a most likely path and a secondary path of the vehicle, and therefrom calculates the desired swivel angles of the headlamps. Based on the values of the swivel angles of each headlamp, the swivel mechanisms cause the headlamps to be appropriately moved.
The controller accesses a map database and uses the vehicle position data to identify the map location of the vehicle. Then, the controller analyzes the map to determine a most likely vehicle path, based on the map location and vehicle heading parameters. The controller then calculates the desired swivel angles of the headlamps based on the calculated most likely path geometry data and if necessary, causes the swivel angles to be changed, i.e. the headlamps to be oriented such that the run of the road determined as the most likely vehicle path is illuminated.
The beam pattern produced in this way includes a defined kink point, whereby the controller determines the kink point position relative to the most likely path. The controller is established to calculate a nominal swivel angle such that the kink point will be at a predefined distance from the center of the vehicle's lane of operation.
In addition, the controller calculates a maximum swivel angle of the headlamps that does not create glare for the oncoming traffic so that the desired swivel angle is determined based on the maximum swivel angle and the nominal swivel angle.
In the predictive adaptive front lighting system disclosed by DE 10 2008 000 769 A1 the beam is directed to a point located on the vehicle path at a constant distance in front of the vehicle. This point is determined based on the geometrical description of the immediately upcoming segment of the road, starting from the current vehicle position.
It is possible, however, that dependent on the altitude profile of the road environment and possible obstacles in form of crash barriers, buildings, trees or the like, the beam pattern resulting from the AFS is obstructed. No optimal road illumination can be obtained due to shadowing resulting therefrom.
It is the problem of the invention to provide an improved method for operating a predictive adaptive front lighting system for a motor vehicle that ensures an optimal road illumination also when the altitude profile of the road environment varies and there are obstacles within the road environment.